This invention relates to development systems for electrostatographic processors and, more particularly, to retractable seals for development systems which are equipped with split housings.
In a conventional electrostatic printing process of the type described in Carlson's U.S. Pat No. 2,297,691 on "Electrophotography", a uniformly charged imaging surface is selectively discharged in an image configuration, thereby providing a latent electrostatic image which is then developed through the application of a finely divided coloring material, called "toner". That process has enjoyed outstanding commercial success, especially in plain paper, xerographic copiers and duplicators. However, it is not limited to xerography or to use in stand alone copiers and duplicators. For example, there are electrostatographic processors which have appropriately controlled stylii for forming the latent image on the imaging surface. Furthermore, it has been found that electrostatographic printing may be advantageously utilized in facsimile systems and computer printers, to name just a couple of its non-copier applications.
Modern electrostatographic processors typically carry out the development process on the fly -- viz., as the imaging surface moves through a development zone. To accomplish that, there normally is a magnetic brush or a cascade development system for circulating a multi-component developer from a sump, through the development zone, and then back into the sump.
As will be appreciated, a multi-component developer is basically a mixture of toner particles and larger so-called "carrier" particles. In practice, the materials for the toner and carrier (or, sometimes, carrier coating) components of the mixture are selected so that they are removed from one another in the triboelectric series, whereby electrical charges of opposite polarities tend to be imparted to the toner and carrier particles when the developer components are blended together. Furthermore, in selecting those materials, consideration is given to their relative triboelectric ranking to the end that the polarity of the nominal charge for the toner particles opposes the polarity of the latent images which are to be developed. Consequently, in operation, there are competing electrostatic forces acting on the toner particles. That is, one set of forces tends to attract them to the carrier particles, while another set of forces tends to electrostatically strip them from that portion of the developer which is brought into the immediate proximity of or actual contact with the image bearing imaging surface.
Experience has shown that the development process is sensitive to any variations in the dimensions of the development zone. For that reason, it has recently been suggested that the development system for an electrostatographic processor should have a split housing so that the development system can be internally accessed for maintenance purposes or the like, without upsetting the development zone (i.e., the interface between the development system and the imaging surface). Copending and commonly assigned United States patent applications on various aspects of that basic concept have been filed by R. E. Smith and H. L. Bresnick under Ser. No. 525,532 now U.S. Pat. No. 3,924,944, issued Dec. 9, 1975 ; R. E. Smith under Ser. No. 525,528 now U.S. Pat. No. 3,981,272, issued Sept. 21, 1976 ; and R. E. Smith and J. E. Forward under Ser. No. 525,530, now U.S. Pat. No. 3,998,537, issued Dec. 21, 1976. Thus, those applications are hereby incorporated by reference.
When an electrostatographic processor is equipped with, say, a cascade or magnetic brush development system, there necessarily are so-called "edge seals" between the imaging surface and the housing for the development system to prevent developer from escaping as it circulates through the development zone. As a general rule, the entire development system is mounted for movement toward and away from the imaging surface. Thus, the edge seals are customarily resilient members which extend forwardly from the housing for the development system to be brought into pressure contact with and retracted from the imaging surface in response to the movement of the development system.